How was the health of Western Lake Erie calculated?
This report card provides a transparent, timely, and geographically detailed assessment of health in Western Lake Erie and it's watershed using data from 2018 defined as the progress of five indicators toward scientifically-derived thresholds or goals. The indicators are combined into two overall health scores, one score for the Lake, and one for the Watershed.
Each sample is compared to a threshold to calculate a score from 0 to 100. All sample scores are averaged for each sampling location to reach a station score. All stations in each region are averaged to a region score. Region scores are area-weighted to get the overall score.
Overall Health Index
The Western Lake Erie report card compares 11 lake indicators (total phosphorus, dissolved phosphorus, nitrate-nitrate, chlorophyll a, walleye, yellow perch, emerald shiner, bloom index, source water toxin, and recreational toxin) and 10 watershed indicators (total phosphorus, dissolved phosphorus, total nitrogen, nitrate-nitrite, source water toxin, total suspended solids, fish, macroinvertebrates, habitat quality, and fish consumption) to scientifically derived thresholds or goals.
Total Phosphorus
Total phosphorus is indicative of too much phosphorus in the water. Phosphorus is an essential nutrient for all plants and animals. However, too much phosphorus in the water causes algae to grow in large, dense blooms, which deplete oxygen for fish and other aquatic organisms. Phosphorus enters rivers and lakes when it is washed off the land, particularly from agricultural lands that have been fertilized.
Dissolved Phosphorus
Dissolved phosphorus is indicative of too much phosphorous in the water. Phosphorus is an essential nutrient for all plants and animals. However, too much phosphorus in the water causes algae to grow in large, dense blooms, which deplete oxygen for fish and other aquatic organisms. Phosphorus enters rivers and lakes when it is washed off the land, particularly from agricultural lands that have been fertilized.
Total Nitrogen
Nitrogen is important to all living things. Nutrients such as nitrogen occur naturally in both freshwater and saltwater. Plants and animals need nutrients to grow and survive. But too much nitrogen in the water fuels the growth of excessive algae, creating dense blooms that block sunlight and reduce oxygen for fish and other organisms. In the lake, total nitrogen was used to assess nitrogen intensity. Total nitrogen is a sum of organic nitrogen as well as ammonia and nitrate-nitrite compounds.
Nitrate + Nitrite
Nitrogen is important to all living things. Nutrients such as nitrogen occur naturally in both freshwater and saltwater. Plants and animals need nutrients to grow and survive. Too much nitrogen in the water fuels the growth of excess algae, creating dense blooms that block sunlight and reduce oxygen for fish and other organisms. Nitrate and nitrite together are of interest because they are the form of nitrogen most available to algae.
Chlorophyll a
Chlorophyll a is the green pigment in photosynthesizing algae that helps them produce food. Measuring chlorophyll is an indicator of the amount of algae in the water, which uses both nitrogen and phosphorus to grow. Too much algae in the water reduces the oxygen available for other organisms, and some algal blooms produce toxins that are harmful to all living things.
Walleye
The walleye is a popular fish for commercial and recreational fishing. The largest walleye population in the world occurs in the Ohio portion of Lake Erie. Increased water pollution in Lake Erie led to a walleye population decline. Lake water quality improved following the Clean Water Act, leading to a walleye resurgence. Population size can be maintained by setting bag limits on commercial and recreational fishing.
Yellow Perch
The yellow perch is a popular fish for commercial and recreational fishing. The yellow perch is common prey for larger species of fish such as the walleye. Yellow perch populations tend to be lower when walleye are abundant, and vice versa. The yellow perch competes for food with the white perch and the invasive zebra mussel, which feeds on the zooplankton that young yellow perch prefer.
Emerald Shiner
The emerald shiner is a small fish that serves as a bait species for fishing. They are important forage for larger sport fish such as the yellow perch and walleye. The emerald shiner diet consists primarily of plankton and small insects. Emerald shiner populations in Lake Erie have been low in recent years, likely due in part to the expanding walleye population.
Bloom Index
The bloom index developed by NOAA measures the severity of an algal bloom based on the biomass of harmful algae and the duration of the bloom. The size of the bloom is largely unrelated to its severity. Some amount of algae in Lake Erie is considered normal and even healthy, because algae provides food for valuable fish species. Blooms that produce toxins, however, are cause for concern and are reflected in the bloom index. Blooms with an index above 5 are considered potentially harmful.
Source Water Toxin
The presence of toxic microcystin, produced by algal blooms, in drinking source water is a threat to human health. Source water toxin indicates that harmful algal blooms have occurred in proximity to drinking water treatment plants. Algal blooms that produce toxins are caused by excessive nutrients, such as nitrogen and phosphorus. The threshold for human exposure to microcystin in drinking water is lower that the threshold of exposure by skin contact.
Recreational Toxin
The presence of toxic microcystin, produced by algal blooms, is a threat to human health when it contaminates water supplies. Recreational toxin indicates that there is enough microcystin in the water to harm humans who come in recreational contact with the water. Recreational contact is primarily skin contact, such as might occur while swimming or kayaking, as opposed to ingestion by drinking.
Total Suspended Solids
Suspended solids in water include a variety of things, from sediments and silt to decaying organic matter. This metric is used as an indicator of water clarity. Generally speaking, clearer water is cleaner water. In Lake Erie, some cloudiness in the water is considered normal because of persistent, non-toxic algae that provides food for fishes and invertebrates.
Fish
Some fish species are more sensitive to environmental degradation than others. The collection of species living in an ecosystem is called an assemblage. Fish assemblages are used as indicators that are sensitive to habitat degradation, environmental contamination, and overall ecosystem productivity. Ecosystems with more fish species tend to be healthier, and the presence of certain, more sensitive species is a sign that the ecosystem is in good health.
Macroinvertebrates
Because they are small, invertebrates are particularly susceptible to environmental contamination. Some invertebrates are more sensitive to environmental change than others. The collection of species living in an ecosystem is called an assemblage. Ecosystems with more species tend to be healthier, and the presence of certain, more sensitive species is a sign that the ecosystem is in good health.
Habitat Quality
What goes on the land eventually ends up in the water. Certain types of land cover, such as forest, are better at reducing runoff into the rivers. Therefore, the quality of terrestrial habitat is an indicator both of current watershed health and of current and future waterways health.
Fish Consumption
The chemical byproducts of industry, such as mercury, are harmful to humans when ingested. These toxins can contaminate fish that reside in polluted rivers and thereby make their way into human diets. Each state within the western Lake Erie basin publishes their own advisories for maximum fish consumption. Cleaner rivers produce healthier fish with fewer consumption advisories, so this indicator is used to measure how clean rivers and lakes are from a human health perspective.
Pesticide
Large-scale agriculture is reliant on the use of chemical pesticides and herbicides to control the onset of pests that would eat the crops and weeds that would out-compete them. However, these chemicals can cause harm to people and animals if they end up in the water supply. Agricultural fields are particularly prone to runoff, and so are likely to leak chemicals into the water. There was not enough data available to score this indicator in any region, but it is an important factor to consider in water quality and overall ecosystem health.